There are numerous situations in which it would be desirable to detect the presence of, and separate the contributions from, multiple sources that compose a wide band signal. For example, it is desirable to detect, localize and classify long range contacts or sources of sound in passive surveillance of the sub-surface ocean. Currently, such information is discerned using two or more physically spaced, directional, multi-channel receivers. Each receiver scans in azimuth across the surveillance area at a single frequency, and plots the power of the received signal; the receiver steps through a number of discrete frequencies in this manner to obtain a directional frequency spectrum. Localization is accomplished by cross-fixing a source detected by the two receivers. The spectrum of each single, localized contact is then compared to a library of the spectral signatures of known contacts for classification. In this case, the spatial information is necessary to permit the separation of the contributors to the wide band signal.
Although such systems are able to detect, localize and classify contacts, they have a number of drawbacks which make them less than ideal solutions to the problem. For one, these systems require two receivers to separate the contributors on the basis of their separate locations. Further, since any single detected source is not necessarily unique to a contact, classification is typically based on a number of detected sources. Therefore, it is necessary to first determine that the multiple sources belong to a single contact. Accordingly, unambiguous classification typically requires that the system first localize the sources by cross-fixing using two directional receivers. Alternatively, a single contributor may be discerned by comparing a multitude of detected sources to a previously-established library of the unique sources associated with known contributors. However, this requires that the emission spectrum of the contributor has been previously mapped and that the sources be loud enough to be clearly dominant. Classification may then be based on the source signals emanating from that single contributor. Accordingly, the detection and classification of contacts requires either equipment redundancy or loud signals plus a library of known contacts. In addition, the multiple-receiver technique is relatively expensive because directionality requires physically large receivers.
There are other situations in which it would be desirable to detect the presence of, and separate the contributions from, multiple sources that compose a wide band signal. For example, in X-ray and radio astronomy it is desirable to detect and classify X-ray and radio sources. However, due to the distances involved it is impossible to determine the range to a source by cross-fixing. Accordingly, to date it has not been possible to unambiguously separate astronomical X-ray and radio sources within a wide-band x-ray and radio source, when they all lie in the same direction in space. It would also be desirable to determine information from EKGs and from brain waves captured by electroencephalograph. To date, however, it has not been possible to use an EEG to predict the onset of an unusual brain event.